Currently there is limited success in achieving full adhesion of biocompatible glasses to the parent metal (e.g., common titanium alloys). Current processes do not yield a consistent ionocovalent bond in the molecular structure, as disclosed in U.S. Pat. No. 8,012,590 to Tomsia et al. Various researchers and technologist have attempted to coat metallic implants with biocompatible glasses using enameling, rapid immersion in molten glass, or plasma spraying techniques. Although some coatings with excellent in-vitro behavior were obtained, the coatings were characterized by cracking and poor integrity of the glass-to-metal interface. These imperfect coatings were due to undesirable covalent oxides inherent in the processing techniques.
Tenacious coatings made with glass on a titanium alloy, or on some other metals, are known to have limited success. There are a variety of defects that could lead to faulty surfaces. For coated metal implants and onplants, a defective coating poses a health risk. A successful coating technology requires that the body not reject or become infected due to the device. Homogeneity of the metal and any coating applied, and continuity of that coding within the design, is required to assure there is no gap for foreign substance; bacteria, viruses, food or the like to lodge and create infection.
Coatings are applied to present a function for the body; be it tissue growth, simulation of tissue (e.g., bone, tooth), or presentation of medications. The coating must be appropriately integrated with the substrate material so that it does not fail by loosening from the substrate (i.e., delamination). Many coated devices are in the field and each has a risk of coating delamination.
One approach to adhering the coating to the metal substrate is by chemically bonding the material to the substrate versus mechanically bonding to the substrate. This is done by preparing both the substrate and biocompatible glass to create an interface that is stronger than previous interfaces attempted by other glass to metal systems.
Accordingly it is a primary object of the present invention to bond biocompatible ceramic (e.g., glass) to a medical device or product in such a way as to minimize delamination.
It is another object to apply biocompatible glass/ceramic to a metallic substrate to produce a homogeneous glass surface upon the substrate without gaps or other defects between the coating and substrate.
It is a more specific object, commensurate with the above-listed objects, to fuse a biocompatible and bioactive ceramic (e.g., glass) to a metal substrate to produce a tenacious coating for a medical product, which is safe and durable to use.